Hydrophone



W. KUNZE Aug. 25, 1936.

HYDROPHONE Filed June 24, 1929 /NVENTOR W/fly Kunze y gJM M /1/3ATTORNEY Patented Aug. 25, 1936 UNITED STATES PATENT OFFICE HYDROPHONEApplication June 24, 1929, Serial No. 373,466

r In Germany July 16, 1928 '7 Claims. (Cl. 177-386) The presentinvention relates to means for detecting sound waves, and moreparticularly to such means for detecting sound waves in water, thoughthe invention may have application in other media. In particular, itrelates to means for the distortionless reception and translation ofsound waves'from acoustic to electrical energy, or even from acoustic tomechanical or to acoustic energy.

Apparatus designed for the same purpose in the prior art first usedametallic diaphragm, but since metallic diaphragms are, for the mostpart, resonant and not aperiodic, they had a resonance peak whichintensified out of proportion the sound at the resonance frequency tothe sounds at other frequencies. Besides this, the resonant metallicdiaphragm responded at its resonance frequency to shocks and blows, notonly distorting the character of the noise-if noise was being listenedto, as is sometimes done in detecting the presence of other ships, bylistening to their propeller noise but also seriously interfering withthe detection of resonant signals.

Rubber diaphragm receivers have been used to overcome'the diflicultiesenumerated above, with remarkably good results.

Also, metallic diaphragms with rubber cushions mounted on the back areused, but apparently while achieving fair results in some cases, theyare not as a rule sufficiently aperiodic to provide a suitable receiver.While purely rubber diaphragms have given good results, it seems thatthe sensitivity of such receivers is not as great as that of receiversusing an all metallic diaphragm.

In my inventiomthesound receiver is not only substantially aperiodic, asthe purely rubber receiver, but appears to be more sensitive, reliable,durable and in general much better fitted for the work for which it isprincipally employed,--as a submarine hydrophone,

The purposes and features of the invention will be more clearlyunderstood by a consideration of the following description of theembodiment of the invention, together with the drawings, in which Figure1 shows a section view of the receiver, and

Figures 2, 3 and 4 show modifications of the inwention.

In Figure 1, represents a casing of the sound eceiver in which there isan electromagnet formed iy the cylindrical shell 2, the core 3 and thecoil III. A cylindrical air gap 4 is formed between the me 3 and theshell 2. ,In this air gap is a movable coil 5, which is made fast by anend piece 4| directly to the diaphragm by means of the bolt 8 and nut42. The diaphragm and coil member is arranged close to the electromagnetso that the coil support may be made as small and light as 5 possible.The core 3 at its end is cupped out at 43 so that the coil 5 may becrowded even closer to its field of useful operation.

In Figure 1, the casing I has an opening 44 and the side wall of thecasing is provided with an inwardly extending flange 45, against theinner surface of which a pad of soft rubber H1, or like material, ispressed. The diaphragm, which presses against the ring III, is composedof two. metallic discs 6 and l fastened together at the 5 center by thebolt 8 and nut 42, and has between the discs a soft rubber disc 9, ordisc of other suitable material, which extends throughout the wholeinner surface of the metallic discs.

On the inner side of the disc I is another ring ll, similar to the ringIll in structure and size and material, but this may be chosen of suchthickness as to space the diaphragm the desired distance from the faceof the electromagnet. The

' whole system, as shown in Figure 1, is held in place by means of thecylindrical shell 2, which may be pressed against the ring H by means ofan end cap 46 threading in the case I. Between the case and the flangeof the cap 46 may be inserted a gasket 41 of suitable material to keepthe device watertight. The end cap 46 serves also to obtain the properpressure desired upon the clamping rings l0 and II, holding thediaphragm in place.

In Figure 2, the electromagnetic system I3 is fixed in the receivingcasing l2. The casing 2 has a flange 48 against which the ring II ispressed. The diaphragm in this case is composed of three membranes l4,l5 and I6, between which are rubber discs l1 and Ill. The diaphragm isheld together at its center by means of the bolt l9 and nuts 49, 50 and5|, the nuts 49 and 50 fixing firmly the structure with the centralmembrane I5. The diaphragm is clamped in place from the front by meansof the rubber ring II), the clamping ring 22 and the externally threadedring 2|, which exerts a pressure against the ring 22. The desiredpressure on the diaphragm edge is obtained by tightening to the desireddegree the ring 2|.

In Figure 3, the outer membrane 23 of the diaphragm is a part of thecasing 24. Behind this outer membrane is a rubber disc 25 and the secondmembrane 26, which is clamped to the first by means of the bolt 21 andnut 28.' The desired it will be noted that the diaphragm operates as .apiston and that the energy picked up by thediaphragm is not first usedin compressing the .rubber disc, as in the case of a purely rubberdiaphragm. In a purely rubber diaphrag before the whole diaphragm takesup a proper oscillation, some of the energy is first used in compressingthe 'rubber nearest the'sound transmitting medium. In the presentinvention, the diaphragm moves as a whole and is then damped by therubber between the two metallic membranes to preserve the truecharacteristic of the note.

The remarkable characteristic of the present diaphragm comes from thefact that, even 2., though aperiodic, it is sensitive to feeblevibrations, that the damping is uniform throughout the'whole diaphragmand less'for feeble vibrations than for large vibrations, that thoughaperiodic it is rigid, and that its mounting be- :10 tween very yieldingclamping rings allows it to move as a real piston diaphragm and stillfurther obtain true aperiodic characteristics without decrease inefficiency of reception.

Besides the above feature, it will be noted that the damping caused bythe rubber disc may be adjustable by loose or tight clamping of themembranes.

Further, the system is so constructed that the vibrations areperpendicular to the membrane 4 surface throughout and, therefore, thedamping is uniform throughout the entire diaphragm area and bending isalso avoided. This relieves edge friction or jamming and consequentdistortion of the diaphragm. In the present construction,

the diaphragm is very easily centered and the whole device assembled,since the diaphragm is one unit and is made to fit exactly in the casingand is centered by the casing walls.

It should also be pointed out that the sensitivity to vibrations can becontrolled and varied by properly dimensioning the size, shape,thickness and materials used for the diaphragm within suitable limits.

While the description above describes the invention in some of itsmodifications, it will be understood that the invention may take other.forms. ,Instead.,of using,,a coil for translating the sound wave toelectrical energy, other means may be used, such as a microphone, orother reslstance varying device, or purely electromagnetic means. Itwill also be noted that other materials than rubber may be used,provided they have the same characteristics for the pure pose herespecified, and that the diaphragm may take other forms orconstructions,provided it fulfills the same objects and purposes as the presentinvention.

Having now described my invention, I claim: 1. A sound receivercomprising a diaphragm composed of a plurality of membranes posttionedparallel, having the exterior membranes of metal material and at leastone of theinterior membranes of softer yielding material, and means foruniting said membranes together at their centers to form a unitaryacting diaphragm, electrodynamic translating means mounted directly onsaid diaphragm and having a fixed course of oscillation, a casing, saiddiaphragm fitting in said casing and having free motion only normally tothe surface of said diaphragm and means for yieldingly holding the edgesof said diaphragm.

2. In a sound receiving structure, a metallic casing having a diaphragmformed as a part thereof, acoustic damping means positioned within thecasing behind the diaphragm, a second diaphragm fitting within thecasing positioned on the other side of said damping means,

means holding said two diaphragms together and means clamping the edgeof the inner diaphragm to the casing.

3. In a sound receiving structure, a metallic casing having a diaphragmformed as a part thereof, a soft rubberdisc filling the portion of thecasing directly behind the diaphragm, a second diaphragm positioned onthe other side of said disc, means pressing said two diaphragms togetherandmeans clamping the edge of the inner diaphragm to the casing.

4. In a sound receiving structure, a metallic casing having a diaphragmformed as a part thereof, a soft rubber disc filling the portion of thecasing directly behind the diahragm, a second diaphragm positioned onthe other side of said disc, a bolt and nut positioned to hold thediaphragms together under tension at their center and'means clamping theedge of the inner diaphragm to the casing.

5. In a sound receiver, a casing, an aperiodic fiat diaphragm composedof' membranes positioned parallel to one another and at one end 01 saidcasing comprising an exterior membrane oi metallic material, an interiormembrane of the same material and a third membrane betweer the two ofyielding material abutting agains1 the interior faces of the othermembranes, mean: passing through the center of the three membranes andclamping them firmly together ant means bearing upon the periphery ofthe oute: side of the inner membrane at the wall of sail casing to clampthe membrane firmly against thl yielding material in the casing.

6. A sound receiver comprising a cylindrica casing having an inwardlyextending flange a one end of the casing, a diaphragm composer of aplurality of membranes positioned paralle to one another and abuttingthe said flange in wardly of the casing, said diaphragm compose of twometallic discs and a yielding disc there between, means for clampingsaid-disc togethe at their centers and clamping means app d a theperiphery of the disc against the flange be hind said discs. I

7. A sound receiver comprising a cyllndrics casingwith a flange formedat one end extend ing inwardly, ,a diaphragm composed of two diselements and a yielding element therebetwee positioned inside saidcasing on the inner sid of said flange, yielding means positioned on botexternal sides of said discs at the edges there and means for clampingsaid diaphragm firm] in said casing.

WILLY KUNZE.

